The present invention relates to a kinetic energy absorption mechanism having applicability to vehicular collapsible steering columns.
Kinetic energy absorption devices are known for use in vehicles to reduce the likelihood of injury in the case of an accident. Such devices come in many different forms. One form that is particularly effective at absorbing significant quantities of energy in a relatively small amount of space employs a plastically deformable member, such as a plastically deformable metal wire or strap, a pusher, and an anvil across which the plastically deformable member is drawn, dissipating energy as the member is deformed. The member is initially bent to form a traveling bight which is positioned over the anvil. As the pusher draws the member over the anvil, the traveling bight travels down the length of the strap.
An example of this technique is described in U.S. Pat. No. 5,788,278, issued Aug. 4, 1998 to Thomas et al., which is wholly incorporated herein by reference. In this patent, a metal strap is formed into a rough M shape with the two legs much longer than the web extending between them. Each leg of the M is positioned on opposite sides of two anvils, and a central pusher is positioned between the two anvils. The pusher is attached to the body of the vehicle, while the pair of anvils are attached to a steering column housing. Upon the instance of a forward collision, the driver is expected to impact the steering wheel which will impart a compressive force on the steering column housing, causing the anvils to move past and on either side of the pusher. The metal strap will be drawn across the anvils as the center is pushed down between them.
Although the use a plastically deformable member is an effective and reliable means for absorbing significant quantities of kinetic energy in a compact space, it has heretofore been impossible to use this technology to adequately vary the amount of resistance in response to various loads. Because vehicular accidents occur with varying degrees of severity, it would be desirable to provide an energy absorption device that will provide a smaller amount of resistance in the case of a less severe collision, and a greater amount of resistance in the case of a more severe collision.
Prior attempts at using a plastically deformable member to vary the amount of resistance with displacement of the steering column housing have been inadequate. This is because the most difficult design performance centers on the desire to begin with a low force level and transition to higher levels. U.S. Pat. No. 5,375,881, issued Dec. 27, 1994 to Lewis, shows in FIG. 2a a metal strap that is utilized in a manner similar to that described above with reference to U.S. Pat. No. 5,778,278 above, but in this case, there are no anvils. Instead, Lewis relies on the bending and tensile strength to keep the xe2x80x9cfreexe2x80x9d ends from buckling under compression while the inner part is under tension, in effect, pulling the bight down. The use of an anvil is preferred, since the effect of friction between the traveling bight and the anvil is desirable, and the risk of buckling is eliminated through the use of anvils.
The strap in FIG. 2a of Lewis has a varying cross section. Specifically, the Lewis strap includes a narrower section in the middle, at the vicinity of the pusher, and wider sections toward the bottom of the opposite legs. Because of the narrower section in the middle, there is a reduced initial resistance which increases when the traveling bight reaches the wider sections. The problem with this design is that the strap may fracture if the transition to the high force exceeds the tensile strength of the narrower section. Since the narrow portions of the strap have just been significantly worked by bending, the tensile strength of the narrower sections may be significantly compromised. Because of the increased resistance due to friction between the anvils and the traveling bights, this risk is heightened if anvils are used.
U.S. Pat. No. 5,026,092, issued Jun. 25, 1991 to Abramczyk, describes an energy absorbing steering column having a passive restraint load limiting column support system adapted to come into play only when the primary energy absorbing system, whatever it may be, fails to provide the energy absorbing controlled collapse of the steering column assembly as designed, or one which is adapted to come into play only upon receiving impact loads of greater magnitude than those for which the system was designed. This system includes a steering column support bracket that is design to fracture under high impact, allowing the steering column to move upwardly in a second degree of freedom. The steering column will then impact the instrument panel, causing its plastic deformation and that of the instrument panel itself, thereby providing additional required energy absorption. (See column 5, lines 10-50 of Abramczyk.) This system does not provide the kind of energy absorption characteristics desired of a collapsible steering column, but rather dispenses with the utility of a collapsible steering column entirely at impact loads greater than a specified threshold.
The disadvantages of the prior art noted above and otherwise are overcome by a kinetic energy absorption device suitable for use with a collapsible steering column that includes a first and second plastically deformable member have a traveling bight, a pusher proximate to a first part of the first member attached to a first body, a catch allowing the second member move a limited distance with respect to the pusher, and an anvil arrangement fixed to a second body. The anvil arrangement is positioned proximate the traveling bights, which have a shape corresponding with an anvil surface of thereof. The anvil arrangement forces the traveling bight of the first member to travel along a length of the first member upon initial relative movement between the first and second bodies, and then forces the traveling bight of the second member to travel along a length of the second member.